PL 700 II Clair Bros Rising from the Ashes

MERRY CHRISTMAS Phase fans!
I have completely separated the transformer from the amp, electrically. Meter board AC and ground disconnected. The bridge with snubbers is still connected to the secondaries. This is the original bridge with metallic case, so it was lifted from the saddle (pictured). There is still about 60 VAC on the centre tap ground bus with reference to my house ground. This voltage voltage decreases to approx 42 volts when the meter is shunted with a 1 Meg resistor. A 10 K resistor reduced the voltage to 0.63 VAC.
I used .3 ufd snubbers. Reliable sources tell me that's not too big, but I will lift them from the bridge just to verify.

PS: I do have Phoenix connectors but the power and ground connections are soldered. I have put #10 screw lugs on the two ground wires for re-attaching to the ground bus.
 

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The transformer core was temporarily shimmed to isolate it from the chassis. IMAX film shims pictured. My analogue AC Ammeter on the variac read 230 mA at 120 VAC with only the bridge and snubbers connected.
Is this normal?
That's about 27 watts. The transformer should get fairly warm but it doesn't. I will leave it on for a couple of hours. If the transformer is more or less a pure inductor with no load on the secondary, does the current lag the voltage by 90 degrees and therefore not heat as much? I think I dozed off in class that day!
 

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Peter S said:
The transformer core was temporarily shimmed to isolate it from the chassis. IMAX film shims pictured. My analogue AC Ammeter on the variac read 230 mA at 120 VAC with only the bridge and snubbers connected.
Is this normal?
That's about 27 watts. The transformer should get fairly warm but it doesn't. I will leave it on for a couple of hours. If the transformer is more or less a pure inductor with no load on the secondary, does the current lag the voltage by 90 degrees and therefore not heat as much? I think I dozed off in class that day!
Click to expand...
It is apparent power, not real power (thus VA ratings, not Watt ratings). The magnetic flux in the core gives it back as the voltage decays. It is called the magnetic charging current.
 
Thanks Joe. I left the transformer connected to 120 VAC, got warm (maybe 105 degrees F) guessing, after 1 hour. Lifted the snubber caps, still 60 VAC on the centre bus. I am now isolating the transformer in my second amplifier in an identical fashion for comparison.
 
Despite the magnetizing current that is flowing which is all apparent power, there is some small real loss due to the small resistance of the primary windings and the magnetic hysteresis loss of the core due to the magnetic poles being shifted back and forth. Both of those are real losses, the magnetizing current is not.
 
Just a quick note, check that the screw for the rubber foot on the transformer cover isn't too long and touching something inside it shouldn't be touching. They can get close to the windings.
 
Peter S said:
All may not be well;
With inputs wired as per WO schematic, sig gen and sacrificial speaker connected, there is a load hum. A slight tingle is felt when touching the chassis or heat fins. Measured approx 60 VAC to my building ground to chassis. Voltage decreases when I touch the chassis. The (leakage) is more or less the same, 10 volts less when I reverse the line cord polarity. Voltage (and hum) are gone when a jumper is connected from the chassis to a wall outlet ground.
The transformer bolts are still insulated from transformer lams and chassis. The transformer itself is not isolated from the chassis. That would possibly require shims between the cast end bell-capacitor saddle and the lamination stack-----if this is even a solution. I gather that it is a good practice to isolate the bolts (prevent eddy currents), but has anyone had to isolate the whole transformer from the chassis?
Fluke meter reads "infinity" from the primary windings to the chassis.
I will search this forum, but has anyone had experience with transformer trouble?
Thanks again, Peter
Click to expand...

I've torn down and built up some seriously beat to shit rusted, dented, and exploded bulk caps, and rats living in 2 pallets of Clair amps and a bunch of non Clair that had the chassis' bent in a horseshoe, but I have never seen a bad transformer (yet). They are tough as hell. Even seen holes in the transformer cover (bondo is a wonderful invention).
 
Well there seems to be more than one turkey in the house tonight! The second amplifier measures the same; with everything disconnected from the bridge except the transformer, the centre tap measures about 60 VAC about earth ground, drops to about 40 VAC when Fluke is shunted by a 1 Meg resistor. This second amplifier is much better (almost perfect) condition and 'sort of' functioned, at least hum was not the issue.
Back to the first amp; first thing coming to mind is the single point chassis ground in the middle of the Left chan back plane.

Very Puzzled, I don't believe both transformers could be leaky----and to the same degree....
 
To be clear---the second Turkey is me, I will double check the grounding scheme.
Merry Christmas, Perry! Thanks for the input, the rubber feet on these two amps are held on by a pop-rivet. I had the rear cover off (to straighten a bend)---and all looked OK inside. Based on both transformers behaving the same, I am hopeful that the problem is my wiring.
 
Peter, your posts are very interesting to me. If I could ask, what are you using for "earth ground"? Have you verified the polarity of the mains wall outlet? Looking forward to hearing how you resolve this issue.
 
Hi Mark;
On my test bench, I am using the wall outlet ground as reference. The ground is several hundred milli-volts away from the neutral, depending on what's drawing current. I am former Theatre sound and projection installer, so understand the star-point grounding necessity. My home theatre rack is has one central ground lug. It is tied to the four-gang outlet box ground. The amplifiers are all mounted with insulating sleeves, washers, and shims. The PL's have always been a PITA to mount! I have been planning to run a direct number 10 ground wire to the hydro ground stake, about a 40 foot length but it hasn't been necessary so far. The system is dead quiet with 3000 watts of amplifier power at the ready.

I don't have access to Hi-pot testing I thought that my test results might give you an idea of the severity of the leakage. As mentioned; both series II amps involved in WOPL'ing are behaving the same. With nothing connected to the amps there is about 60 VAC from the chassis to the wall outlet ground. With the Fluke meter shunted by 1 meg, it drops to about 40 VAC. 10 k shunt drops it to 650 mV AC. My thinking is that grounding the chassis would solve this issue? Maybe just mounting them to the rack without isolation?

After all the output devices were installed, I was anxious to hear the amp produce a sound through a speaker. The amp's only connection to ground was the signal gen, and that was the INPUT ground. I could see this as the issue---huge hum and faint sine wave in the background. I will re-connect everything and try grounding the chassis for another speaker test. I actually had envisioned replacing the 6-32 screw for the single point chassis connection, with a 6-32 long stud to create an external ground connection.....Or running a wire from one of the speaker ground terminals to the rack star-point ground (some contradiction to the amp's internal star-point scheme with that brain-burp).
Just puzzled that no one has had this leakage issue, I will search this forum for anything relevant.
Happy New Year All!

PS; pictured is my quasi-comp 700B driving the mid-range line arrays, to be replaced by one of the WOPL'ed series II's.
 

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Peter S said:
Hi Mark;
On my test bench, I am using the wall outlet ground as reference. The ground is several hundred milli-volts away from the neutral, depending on what's drawing current. I am former Theatre sound and projection installer, so understand the star-point grounding necessity. My home theatre rack is has one central ground lug. It is tied to the four-gang outlet box ground. The amplifiers are all mounted with insulating sleeves, washers, and shims. The PL's have always been a PITA to mount! I have been planning to run a direct number 10 ground wire to the hydro ground stake, about a 40 foot length but it hasn't been necessary so far. The system is dead quiet with 3000 watts of amplifier power at the ready.

I don't have access to Hi-pot testing I thought that my test results might give you an idea of the severity of the leakage. As mentioned; both series II amps involved in WOPL'ing are behaving the same. With nothing connected to the amps there is about 60 VAC from the chassis to the wall outlet ground. With the Fluke meter shunted by 1 meg, it drops to about 40 VAC. 10 k shunt drops it to 650 mV AC. My thinking is that grounding the chassis would solve this issue? Maybe just mounting them to the rack without isolation?

After all the output devices were installed, I was anxious to hear the amp produce a sound through a speaker. The amp's only connection to ground was the signal gen, and that was the INPUT ground. I could see this as the issue---huge hum and faint sine wave in the background. I will re-connect everything and try grounding the chassis for another speaker test. I actually had envisioned replacing the 6-32 screw for the single point chassis connection, with a 6-32 long stud to create an external ground connection.....Or running a wire from one of the speaker ground terminals to the rack star-point ground (some contradiction to the amp's internal star-point scheme with that brain-burp).
Just puzzled that no one has had this leakage issue, I will search this forum for anything relevant.
Happy New Year All!

PS; pictured is my quasi-comp 700B driving the mid-range line arrays, to be replaced by one of the WOPL'ed series II's.
Click to expand...

And your 700B? No similar problem?
 
Have you taken all 4 bolts out of the transformer to see if any of your effect is coming from that?
 
I did not remove the bolts but I tested each bolt and found no continuity to the laminations or chassis. I have loosened the bolts, put shims between the transformer, saddle, and chassis. Checked; all no contact. Found 62 VAC (same) on centre bus, 33 V on chassis, 31 V on saddle, and 26 V on the lam stack.
Could this not be some kind of inductive or capacitive coupling with all that stray magnetic flux? How can there be 31 Volts on the saddle when it was completely isolated. Maybe the guy who sold these amps to me was a lot smarter than I gave him credit for!
 
The quasi 700B (you helped me fix the ringing problem) has a WO control board, 2012 vintage, not sure what rev. No hum issues but once accidentally plugged in the RCA cable with the amp on--I thought the voice coils were going to leave the building! I believe with the centre pin of the RCA plug making contact before the shell, wouldn't any free-floating leakage be interpreted as signal for that brief moment? Regardless, the amp is dead quiet with the only RCA lines in as ground connection. The amp is dead quiet but has the original PL ground scheme and I have bypassed the volume pots.
 
Peter S said:
The quasi 700B (you helped me fix the ringing problem) has a WO control board, 2012 vintage, not sure what rev. No hum issues but once accidentally plugged in the RCA cable with the amp on--I thought the voice coils were going to leave the building! I believe with the centre pin of the RCA plug making contact before the shell, wouldn't any free-floating leakage be interpreted as signal for that brief moment? Regardless, the amp is dead quiet with the only RCA lines in as ground connection. The amp is dead quiet but has the original PL ground scheme and I have bypassed the volume pots.
Click to expand...

As asking if you measure any AC voltage on that chassis Peter.
 
Gepetto said:
As asking if you measure any AC voltage on that chassis Peter.
Click to expand...


Why would you use the wall outlet as reference ground??? The 700 has a 2 prong non polar plug and the ground is not used. If you are using an IEC outlet on the amp, the ground is not used, only the hot and return........ Sorry Joe, that was not directed to you.....
 
Perry;
The secondary centre tap is 60 VAC above earth ground. The wall outlet ground is my simplest connection to earth ground and only a temporary measurement. I very much appreciate all advice but please follow the thread closely. The chassis has an undeniable spurious voltage on it.
What would you use as a reference point?
 
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